1. Field of the Invention
The present invention relates to a process for producing an original hologram film. More particularly, the present invention relates to a process for producing an original hologram film free from decrease in diffraction efficiency that is brought about when the wavelength at which the diffraction efficiency of a hologram reaches its peak (hereinafter referred to as the diffraction peak wavelength) shifts due to, for example, the shrinkage of a volume-hologram-recording photosensitive material; to such an original hologram film; and to a hologram duplication process using the same.
2. Description of the Related Art
Heretofore, it has well been known that a volume hologram capable of being regenerated by white illuminating light is recorded by allowing scattered light from a light-scattering object and a reference wave to interfere in a volume-hologram-recording photosensitive material. Also well known is the following process for duplicating an original volume hologram (hologram duplication process): a volume-hologram-recording photosensitive material is superposed on a reflection- or transmission-type volume hologram (original hologram), and laser light is allowed to enter into this combination either from the photosensitive material side or from the original hologram side, thereby allowing the incident light and the light diffracted by the volume hologram (original hologram) to interfere in the photosensitive material to duplicate therein the original volume hologram.
When a photopolymer or the like is used as the photosensitive material for recording a volume hologram, the following may occur. Namely, the photosensitive material shrinks after the volume hologram has been recorded, and the spacing of the interference fringes recorded in the photosensitive material decreases; consequently, the diffraction peak wavelength shifts to the shorter wavelength side. For this reason, when it is tried to duplicate such a volume hologram by using a duplicating beam whose wavelength is the same as that of the photographing beam which is used when an original hologram is made, the diffraction efficiency is decreased, and it becomes difficult to efficiently duplicate the original hologram.
In order to compensate for the shift of the diffraction peak wavelength that is brought about due to the shrinkage of the photosensitive material, the correction of angle has conventionally been made by making the incidence angle of the duplicating beam smaller than that of the reference beam used for recording the original hologram so that the wavelength of the duplicating beam will agree with the diffraction peak wavelength.
However, when the diffraction peak wavelength for the original hologram is corrected by means of the above-described correction of angle, the visible area of the hologram duplicated may be restricted (see Japanese Patent Application No. 75498/1998 (Japanese Patent Laid-Open Publication No. 340038/1998)). Moreover, depending on the quantity of the shift, there may be such a case that it is impossible to make such a correction.
In the light of the foregoing problems, the present invention has been accomplished. An object of the present invention is therefore to provide a process for producing an original hologram film free from decrease in diffraction efficiency that is brought about when the diffraction peak wavelength shifts due to, for example, the shrinkage of a volume-hologram-recording photosensitive material. Another object of the present invention is to provide such an original hologram film. A further object of the present invention is to provide a hologram duplication process using this original hologram film.
We have already described the following in the specification of Japanese Patent Application No. 308675/1998 duly filed with the Japanese Patent Office. Namely, it is possible to obtain a reconstructed beam whose wavelength is almost the same as that of a recording beam by incorporating, into an adhesive layer, the same migrating ingredient as that incorporated into a volume-hologram-recording layer made from a photopolymer, thereby preventing change of the migrating ingredient in the volume-hologram-recording layer; and it is also possible to control the wavelength of the reconstructed beam in this manner. The present invention utilizes this means of controlling the wavelength of a reconstructed beam, which we ourselves have proposed.
The present invention provides a process for producing an original hologram film, comprising the steps of: preparing a hologram-recording film having a recording layer of a volume-hologram-recording photosensitive material in which a volume hologram has been recorded, and a film for controlling the wavelength of diffracted light, having a material layer containing an ingredient which can migrate to the recording layer to shift the diffraction peak wavelength for the volume hologram recorded in the recording layer; and affixing the film for controlling the wavelength of diffracted light to the hologram-recording film with the recording layer and the material facing each other.
The present invention also provides an original hologram film comprising: a recording layer of a volume-hologram-recording photosensitive material layer in which a volume hologram has been recorded; and a material layer laminated to the recording layer, wherein the material layer contains an ingredient which can migrate to the recording layer to shift the diffraction peak wavelength for the volume hologram recorded in the recording layer.
A photopolymer is used for forming the recording layer for use in the present invention. The material layer for use in the present invention is made from an adhesive agent. Polypropylene glycol is incorporated into the material layer as the ingredient that can migrate to the recording layer to shift the diffraction peak wavelength for the volume hologram recorded in the recording layer.
Also provided by the present invention is a process for duplicating a hologram, comprising the steps of: preparing an original hologram film including a recording layer of a volume-hologram-recording photosensitive material in which a volume hologram has been recorded by using a photographing beam having a predetermined wavelength, and a material layer laminated to the recording layer, containing an ingredient which can migrate to the recording layer to shift the diffraction peak wavelength for the volume hologram recorded in the recording layer; and placing a hologram-recording film on the original hologram film; and recording, in the hologram-recording film, the volume hologram that has been recorded in the original hologram film, by using a duplicating beam having a predetermined wavelength.
In the hologram duplication process of the present invention, a beam having the same wavelength as that of a photographing beam can be used as the duplicating beam. In this case, the ingredient having the above-described function is incorporated into the material layer in such an amount that the shift of the diffraction peak wavelength to be brought about due to the shrinkage of the recording layer can be compensated. Further, in the hologram duplication process according to the present invention, a beam having a wavelength different from that of a photographing beam can be used as the duplicating beam. In this case, the above specific ingredient is incorporated into the material layer in such an amount that not only the shift of the diffraction peak wavelength to be brought about due to the shrinkage of the recording layer but also one to be brought about due to the difference between the wavelength of the duplicating beam and that of the photographing beam can be compensated.
According to the present invention, an original hologram film is made by laminating, to a recording layer of a volume-hologram-recording photosensitive material in which a volume hologram has been recorded, a material layer containing an ingredient capable of migrating to the recording layer to shift the diffraction peak wavelength for the volume hologram recorded in the recording layer. Therefore, even in the case where the diffraction peak wavelength shifts due to, for instance, the shrinkage of the recording layer, it is possible to efficiently duplicate the original hologram without suffering from decrease in diffraction efficiency. Further, according to the present invention, it is also possible to duplicate a hologram by using a duplicating beam whose wavelength is different from that of a photographing beam. The duplication of a hologram can thus be conducted efficiently irrespective of the wavelength of a duplicating beam.